Skimming mechanism for centrifuges



April 1934- s. c. LINDBERG 1,954,676

SKIMMING MECHANISM FOR CENTRIFUGES Filed Aug, 28. 1931 2 2 4 5 320% fill/[425230 Patented Apr. 10, 1934 PATENT OFFICE smmmo m-zcnamsu ron csu'mmoess Sven O. Lindberg, Mansfield, Mam, asslgnor, by mesne assignments, to Centrifugal Engineering and Patents Corporation, Jersey City, N. 1., a corporation of New Jersey Application August 28, 1931, Serial No. 559,880

6 Claims.

This invention relates to apparatus for separating from liquids particles of specific gravity differing from that of the liquid. The embodiment of the invention illustrated on the drawing 5 and hereinafter described in detail is more especially intended for the purification of aqueous suspensions of cellulosic pulp such as are used in the manufacture of paper. Liquids of this type usually consist of water in which are suspended pulp fibers having a specific gravity very close to that of water so that they can be kept in suspension by slight agitation. Pulp stock, whether made of rags, wood, or other material, is usually liable to contain impurities of various kinds, many of these impurities being particles of specific gravity differing only slightly from that of the pulp stock. For the manufacture of many articles such as high grade writing papers it is highly essential that the pulp stock be refined so that when it is made up into paper, it shall be substantially free from impurities of any kind. The purification of pulp stock may be efficiently accomplished by passing the stream of stock through a suitable centrifuge designed for such purpose. Such a centrifuge may consist of a vertical drum' capable of being rotated at a considerable speed, preferably in the neighborhood of 600 R. P. M. A stream of pulp stock is supplied to the lower end of the drum and flows upwardly to the upper end of the drum, the stock being held against the wall of the drum during this flow by reason of the strong centrifugal force resulting from the rotation of the drum. One or more annular ribs are provided in the drum projecting inwardly to form a series of pools across which the pulp stock stream must flow. Particles of greater density than that of the pulp are caught in these pools by reason of the centrifugal force acting thereon. A skimming ring is provided in the upermost pool to catch the particles of lighter density which tend to float on the surface of the pool. The period of time during which the drum may be operated satisfactorily for the removal of impurities from the pulp stock depends upon various factors such as the amount of stock supplied to the drum and the percentage of impurities originally in the stock. If this percentage runs high, the capacity of the drum to re move impurities from the stock stream may diminish seriously in an hour or so. With the average run of pulp stock, the drum may be operated satisfactorily for several hours without being cleaned out. Since it is undesirable to stop the drum for cleaning purposes any more frequently than is necessary, on account of the loss of time and effort involved, it is a purpose of this invention to provide for the periodic removal of impurities of low specific gravity. To this end structure is provided whereby the floating impurities may readily be removed from the drum '0 without interrupting the operation thereof. This is accomplished by so regulating the skimming ring that the normal level of the pool is above, that is, radially inward with respect to, the inner diameter of the skimming ring so that stock in cl the uppermost pool in the. drum tends to flow over the inner periphery of the ring. To prevent such flow during the ordinary operation of the drum, I may provide an auxiliary ring which is movable in respect to the skimming ring and which normally is in contact therewith, the movable ring being arranged to project radially inward with respect to the skimming ring. When the movable ring is in contact with the skimming ring, it acts as a crest of a dam to hold back the surface waters of the adjacent pool. I provide means for moving the movable ring away from the skimming ring during the operation of the drum. This leaves a clearance between the skimming ring and the movable ring, through which the surface waters of the pulp stock may flow. Provision is made to catch these surface waters which contain practically all of the lighter impurities, and to lead the surface waters away to the place of suitable disposal. For a more complete understanding of the invention reference may be had to the embodiment thereof hereinafter described and illustrated on the drawing which shows a sectional view of a centrifuge embodying the invention.

Referring to the drawing in detail, 10 represents a drum which may be of any suitable shape, a cylindrical drum being shown herein. This drum is mounted on a vertical shaft 11 which is connected by a. suitable flexible coupling 12 with a source of power 13 such as an electric motor as shown, or a power pulley. The drum 10 has a wide lower flange 14 so that when pulp stock is introduced into the lower end of the drum, it necessarily flows upward along the wall of the drum. A pair of annular ribs 15, 16 extend inwardly from the wall of the drum, suitable pools of pulp stock being formed below these ribs. At the upper end of the drum is an inwardly projecting flange 17 below which is formed the upper- 5 most pool in the drum. The drum is supplied in a stream through a supply channel 20 which empties into a hopper 21. The lower end of the hopper discharges the stock into the interior of a conical member 22 which is supported on a conlcal frame 23, by which the drum 10 is mounted on the shaft 11. The conical member 22 rotates with the drum so that as the pulp stock descends into the supply member 22 it is held against the inner surface thereof by the centrifugal force of rotation. The conical member 22 discharges the pulp stream at its lower end into the lower end of the drum, whence it flows upwardly over the ribs 15, 16 until it enters the pool below the flange 17. Supported on the rim of the drum for rotation therewith is a skimming member 25 in the form of a ring having an annular portion 26 with a cylindrical flange 2'? extending beneath the surface of the pool, that is, radially outward. The upper face of the annular portion 26 is adjustably spaced from the inner edge of the flange 17, this inner edge being preferably formed with a slight bead as shown. By adjusting the skimming ring axially, the clearance between the annular portion 26 of the skimming ring and the bead edge of the flange 17 may be accurately controlled. If the rate of supply and character of the stock supplied to the centrifuge are maintained substantially constant, the depth of'the uppermost pool can be controlled by the adjustment of the skimming ring 25 with reference to the flange 17. Thus by moving the skimming ring slightly upward, the clearance may be decreased and the consequent depth of the pool may be increased. According to the present invention I adjust the skimming ring so that the pool will be of sufficient depth to overflow that portion of the ring which is secured to the drum. If the drum is then operated, part of the stock stream will pass under the skimming ring and through the clearance between the skimming ring and the flange 1'7. Another portion of stock will be discharged over the skimming ring. In order to keep these two lines of discharge separate, I may provide a circular trough 30 for the pulp which passes through the clearance between the skimming ring and the flange and which escapes over the upper face of the'flange. A second trough 31 may likewise be provided to receive and collect the pulp which is discharged over the skimming ring 25, that is, which passes through the opening formed by the ring 25. To facilitate the collection of this surface stream of pulp, the ring 25 may be provided with an upwardly extending portion 32 terminating in a suitable lip 33, a trough 31 surrounding this lip and receiving pulp which is flowing outwardly from this lip by centrifugal force.

Ordinarily impurities of light density are not present in pulp stock in suflicient quantity to warrant a constant discharge of a surface stream of stock to carry off these impurities as hereinbefore described. Such operation would in most cases be wasteful. Hence I provide an auxiliary ring which normally engages the lip 33 and ordinarily acts as a part of the skimming ring 25. This auxiliary ring 35 projects radially inward from the lip 33 so that while it is in contact with the lip it acts as a dam to prevent the escape of any stock over the ring 25 and into the trough 31. Thus, with the ring 35 in position as shown in the drawing, the uppermost pool of pulp stock is backed up behind the ring 35 so that it escapes only under the skimming ring 25 and into the trough 30. During such operation the lighter impurities tend to float upon the surface of the pool and to collect at the upper end thereof, that is, adjacent to the ring 35, the purified pulp passing outside of the skimming ring and through the clearance between this ring and the flange 17. At suitable intervals varying according to the percentages of light impurities in the pulp, the ring 35 may be lifted clear of the lip 33. This creates a clearance between these two members for the discharge of the surface portion of the uppermost pool. Since practically all of the light impurities which collect during the operation of the drum have gathered on the surface of the pool adjacent to the ring 35, these impurities are quickly swept into the trough 31 by the surface current which flows over the lip 33. Thus, after a brief period of operation with the ring 35 raised, this ring may again be lowered into contact with the lip 33 to prevent further discharge over the lip until more of the light impurities have had time to collect.

For the operation of the ring 35 during the rotation of the drum, I may connect this ring with a suitable collar 36 as by a number of radial arms 37. The collar 36 is adapted to rotate freely about the hopper 21 and is provided with a peripheral groove 38 in which ride a pair of pins or rollers 40 carried by links 41 which depend from a lever 42. The lever may be pivotally mounted as at 43 on the hopper and may be provided with a handle 44 for convenient operation. Thus, by raising the handle 44, the ring 35 is lifted clear of the lip 33. By releasing the handle 44, the ring 35 is allowed to descend by gravity into contact with the lip 33. Thus the cleansing efficiency of the centrifuge may be easily maintained as far as the light impurities are concerned, by periodically raising the ring 35 for brief intervals to discharge the surface impurities from the uppermost pool within the drum. This involves only a negligible loss of pulp and maintains the operation of the centrifuge at a high eificiency.

It is obvious that various changes in form and structure may be made in the embodiment of the invention herein shown and described without departing from the spirit and scope of the invention as defined in the following claims.

I claim:

1. Apparatus of the class described comprising a rotatable drum, means for introducing a stream of liquid into said drum during rotation thereof, means for obstructing the flow of liquid within said drum to form a pool against the wall thereof, said obstructing means including a skimming ring having a fixed portion normally submerged in said pool and a movable portion normally engaging said fixed portion and projecting radially inward therefrom, and means for moving said movable portion from engagement with said fixed portion whereby liquid in said pool may flow between said portions.

2. Apparatus of the class described comprising a rotatable drum, means for introducing a stream of liquid into said drum during the rotation thereof, means for obstructing the flow of liquid with the drum so as to form a pool therein against the wall of the drum, said obstructing means including a damming device composed of two normally contiguous rings, one of said rings being fixed to the drum with clearance between it and the rim of the drum for the flow of liquid, and adjusted relatively to said drum to maintain the surface of said pool radially inward of said ring, the other ring normally projecting radially inward from the fixed ring further than the surface of the pool, and means for moving said other ring from contact with said fixed ring during rotation of the drum to provide clearance between the rings for the flow of stock over said flxed ring.

3. A centrifuge for purifying aqueous pulp stock or the like, which comprises a rotatable drum, means for introducing a stream 01' stock into the lower end of said drum during rotation thereof, an inwardly projecting flange at the upper end of said drum below which a pool of stock is formed during the rotation of the drum, a skimming ring having an annular portion projecting below the surface of said pool, said ring also having a portion projecting axially above said flange, means for adjusting said ring relatively to said flange to regulate the depth of the pool, a movable ring normally engaging said skimming ring and projecting radially inward therefrom, and means for moving said movable ring to form a clearance between said rings for the flow of stock.

4. A centrifuge for purifying aqueous pulp stock or the like, which comprises a rotatable drum, means for supplying a stream of stock into the lower end of the drum, an inturned flange at the upper end of the drum beneath which a pool of stock is maintained during the operation of the drum, a skimming ring mounted on said drum and adjustable relatively to said flange to regulate the depth of said pool, said ring having an annular portion near said flange and an axially extending portion projecting above said flange and terminating in a lip, a movable ring normally engaging said lip and projecting in wardly therefrom, means for moving said movable ring from said lip during operation of the drum to permit flow of stock between said rings and over said lip, a pair of separate circular troughs surrounding the upper end of the drum and arranged to catch the stock which flows over said flange and lip respectively.

5. Apparatus of the class described, comprising a rotatable drum, an inturned flange at the upper end of said drum, a skimming ring adjacent to and spaced from said flange, said ring having a portion radially inward of said flange and projecting upwardly above the flange, and a second ring movable into and out of contact with said skimming ring, said movable ring extending radially inward of said skimming ring, and means actuable during the rotation of the drum to move said movable ring into or out of contact with said skimming ring.

6. Apparatus for purifying aqueous pulp stock or the like, comprising a rotatable drum having an inturned flange at its upper end for the retention of a pool of stock within the drum, a skimming ring having an annular portion adapted to project below the surface of said pool, said ring having another portion extending axially above the inner edge of said flange, an auxiliary ring engageable with the upper edge of said skimming ring and extending radially inward therefrom, means for moving said ring into and out of engagement with said skimming ring for intermittent discharge of stock over the upper end of the skimming ring, a trough surrounding the upper end of the drum to receive stock discharged over the flange thereof, and a separate trough surrounding the upper end of said skimming ring to receive stock discharged therefrom.

SVEN C. LINDBERG. 

